1. Technical Field
The present invention is related to a method of manufacturing a printed circuit board.
2. Description of the Related Art
In step with the trends toward higher-speed and higher-integration semiconductor package substrate and with the method of connection with a semiconductor developing from the conventional wire bonding to the new flip-chip bonding, there is a growing demand for application of different types of surface treatment on a single printed circuit board. Moreover, a more precise design is required for a certain area of the printed circuit board than other areas.
To address the demands for a design that applies different types of surface treatment to one substrate or enhances the precision of a certain area, it is needed to develop an improved method that is different from the conventional method.
FIGS. 1 to 8 show the process flow of a method of manufacturing a printed circuit board in accordance with the related art. In the conventional technology, an etch-back process is used to perform different surface treatments for a wire bonding pad and a solder ball pad of the printed circuit board for semiconductor package described above. First, as illustrated in FIGS. 1 and 2, an opening is formed on a solder resist layer 15 such that a wire bonding pad 12, a solder ball pad (not shown) and a plated bus-line 14 formed on an insulation layer 11 can be exposed to the outside.
Then, as illustrated in FIGS. 3 and 4, the surfaces of the solder ball pad (not shown) and the plated bus-line 14 are covered by a plating resist 16, and a nickel layer 17 and a gold layer 18 are formed only on the surface of the wire bonding pad 12 by way of electroplating.
Then, as illustrated in FIGS. 5 to 8, after the plating resist 16 is removed, the surfaces of the solder ball pad (not shown) and the wire bonding pad 12 are covered by an etching resist 19, and the plated bus-line 14 is removed. Then, the etching resist 19 is removed.
Finally, an organic solderability preservative (OSP) layer is formed on the solder ball pad (not shown).
In the conventional technology, however, a plating resist for covering a solder ball pad and an etching resist for removing a plated bus-line are needed, increasing the number of production processes, the production time and the defect rate.
Also, since the plated bus-line is required for electroplating, disposing the circuits and pads is restricted. Although the plated bus-line is removed by the etch-back process described above, the plated bus-line would leave a residual part, as illustrated in FIG. 8, causing a noise when transmitting high-speed signals.
Therefore, surface treatment on the wire bonding pad by way of electroless plating has been attempted, but since a conventional plating resist can not survive in a plating solution for electroless plating, there has been a difficulty in employing surface treatment, for example, OSP, which is different from the one employed on the wire bonding pad, on the solder ball pad.